1. Field of the Invention
The present invention relates to a printing press for doing printing such as offset printing in which inks are applied to printing plates to form ink images, which are then transferred onto printing paper. And especially, the present invention relates to a printing press equipped with a color chart measuring apparatus for reading a color chart printed on printing paper to acquire color chart information.
2. Description of the Background Art
Recently, printing presses which install therein a plate making machine (printing plate recording apparatus) for forming an image on a printing plate on the basis of digital image data, known as a CTP (computer-to-plate) machine, have been developed for commercial use. Such printing presses are called digital printing presses and are suitable for short-time print jobs such as multi-kinds, small-circulation printing, since they can produce printed matter directly from image data. Those digital printing presses have automatized a prepress process for ease of handling by even inexperienced operators, but still further automation of a printing process, such as ink feed control, is desired.
For the control of ink feed, conventional printing presses have generally used a separate type color measurement table for measuring a picked-up printed sample placed thereon. This, however, requires an operator to pick up an appropriate printed sample for color measurements of printed matter.
To solve this problem, printing presses comprising means for capturing an image of printing matter have been proposed. According to this conventional technique, the printing press obtains image data through imaging of printing matter on its impression cylinder and compares this image data with previously-obtained reference image data about reference printing matter for ink feed control. In this conventional technique, an image of printing matter is captured within the printing press, which brings the advantage of avoiding operator involvement which would be required when using the color measurement table.
The above conventional technique, however, has a problem that reading and comparing a whole image of printing matter with a reference image requires handling of a large amount of image data and requires much time for image data processing. In addition, the preparation of a reference image is not suitable for print jobs which require immediacy, such as multi-kinds, small-circulation printing.
The present invention is intended to solve the aforementioned conventional problems, and an object thereof is to provide a printing press equipped with a color chart measuring apparatus for providing a color chart on printing matter, instead of reading a whole image of the printing matter, and then reading and measuring only an area relating to the color chart on printing paper being transported. In this case, the amount of image data to be handled can be reduced and the use of the color chart avoids the necessity of preparing a reference image.
The present invention is especially suitable for a printing press equipped with a printing plate recording apparatus for recording an image on a printing plate, such as digital printing presses as above described. It provides a printing press capable of setting an area to read a color chart according to the recording position of the color chart in image recording.
Another object of the present invention is to provide a color chart that allows precise measurement and to provide a color chart measuring method and apparatus capable of measuring a color chart on printing paper being transported with high accuracy even if flapping or the like of the printing paper being transported causes variations in the imaging level in different parts of the printing paper.
A first aspect of the present invention is directed to a printing press for printing a color chart including a plurality of color chart fields in a margin of printing paper, said printing press equipped with a color chart measuring apparatus for reading each of the color chart fields on the printing paper to measure color chart information. The printing press comprises: a transport section for transporting the printing paper; an imaging section for capturing an image on the printing paper transported by the transport section; a reading time setting section for determining, in accordance with a transport operation of the printing paper, a reading time during which the imaging section reads an image of the color chart; an image data storage section for storing image data on an area read by the imaging section during the reading time, as readout image data; a color chart actual position calculation section for calculating an actual position in which each of the color chart fields was actually printed, on the basis of the readout image data; and a color chart information determination section for determining color chart information about each of the color chart fields from the readout image data corresponding to the actual position.
In the first aspect, the imaging section can read only an area including the color chart, which reduces the amount of image data to be handled. Further, the use of a preset color chart avoids the necessity of preparing a reference image for comparison.
According to a second aspect of the present invention, the printing press of the first aspect further comprises: a printing plate recording section for positioning and recording the color chart on a printing plate, wherein the reading time setting section determines the reading time on the basis of a position in which the color chart was recorded.
In the second aspect, the reading time to read the color chart can appropriately be determined according to the recording position of the color chart in image recording.
According to a third aspect of the present invention, the printing press of the second aspect further comprises: a color chart data adding section for adding color chart data representing the color chart to print image data representing printing matter; and a color chart position computation section for computing a position to which the color chart data was added, on the basis of an image size given by the print image data, wherein the reading time setting section determines the reading time on the basis of the position to which the color chart data was added.
In the third aspect, the position of the color chart is computed in response to an image size given by the image data, which allows proper setting of the reading time responsive to variations in the image size.
According to a fourth aspect of the present invention, the printing press of the first aspect further comprises: a plate cylinder for holding a printing plate; a blanket cylinder with a blanket surface for receiving an ink image from the plate cylinder; an impression cylinder for holding printing paper and receiving an ink image from the blanket cylinder; and an encoder for detecting a rotational position of at least any one of the impression cylinder, the plate cylinder, and the blanket cylinder, wherein the reading time setting section determines the reading time on the basis of a detection signal from the encoder.
In the fourth aspect, the reading time is determined by the encoder for detecting the rotational positions of the cylinders, which eliminates the need for additional means for detecting the position of printing paper.
According to a fifth aspect of the present invention, in the printing press of the fourth aspect, the plate cylinder and the blanket cylinder are double-diameter cylinders each having two print areas, and the impression cylinder is an n-fold diameter cylinder having a n/2-fold diameter of the plate cylinder (where n is a natural number). The printing press feeds and delivers the printing paper for every two turns of the impression cylinder, and further comprises: a paper feed/delivery signal setting section for setting a paper feed/delivery signal that indicates whether or not to feed/deliver the printing paper for each rotation of the impression cylinder, wherein the encoder detects a rotational position of the impression cylinder, and the reading time setting section determines the reading time by determining from the paper feed/delivery signal a time when the printing paper passes under the imaging section and determining from the detection signal from the encoder a position of the printing paper being transported.
In the fifth aspect, even if the printing press feeds printing paper for every plurality of turns of the impression cylinder, the reading time can be determined for only printing paper being transported.
According to a sixth aspect of the present invention, in the printing press of the first aspect, the color chart includes one or more reference marks to specify the position of the color chart, the color chart actual position calculation section calculates the actual position of each of the color chart fields, on the basis of both a position of the reference mark detected according to the readout image data and previously-stored position information about relative positions of the reference mark and each of the color chart fields.
In the sixth aspect, the color chart includes the reference marks, which facilitates detection of the position of the color chart and thereby improves the accuracy of detecting the position of each of the color chart fields.
According to a seventh aspect of the present invention, in the printing press of the sixth aspect, the imaging section includes two line sensors arranged along a direction of print span, each sensor being capable of reading an area on the color chart, the areas to be read by both of the line sensors overlapping each other, and at least one of the reference marks is a common reference mark which is positioned in an overlapping portion of the areas to be read by both of the line sensors and is used in common for reading of the areas.
In the seventh aspect, even when the imaging section is divided into two parts, a common reference mark allows alignment of image data read by each imaging section. This reduces the number of reference marks in the color chart.
According to an eighth aspect of the present invention, in the printing press of the seventh aspect, the image data storage section includes two memories for individually storing two readout image data obtained by the two line sensors, each of the two readout image data being stored in a corresponding one of the memories from the other side of the common reference mark.
In the eighth aspect, image data read by the two imaging sections can be stored in the memories in the same address direction with respect to a common reference mark. Thus, the two image data can be processed according to the same procedure.
A ninth aspect of the present invention is directed to a printing press for printing a color chart having a plurality of color chart fields in a margin of printing paper, said printing press equipped with a color chart measuring apparatus for reading each of the color chart fields on the printing paper to measure color chart information. The printing press comprises: a measuring area setting section for determining an area in which the color chart is located on the printing paper as a measuring area; a paper stack section for stacking the printing paper printed; a rough positioning section for roughly positioning the printing paper stacked in the paper stack section; an imaging section for reading an image on the printing paper; an image data storage section for storing, out of readout image data obtained by the imaging section, at least readout image data on an area determined by the measuring area setting section; a color chart actual position calculation section for calculating an actual position of each of the color chart fields on the basis of the readout image data; and a color chart information determination section for determining color chart information about each of the color chart fields from the readout image data corresponding to the actual position.
In the ninth aspect, reading is performed on delivered printing paper at rest, which eliminates the need for a mechanism for stabilizing the transportation of printing paper for reading.
A tenth aspect of the present invention is directed to a printing press for doing printing using a printing plate on which an image is recorded. The printing press comprises: a color chart data storage section for storing color chart data representing a color chart; a color chart data adding section for adding the color chart data to print image data; a printing plate recording section for recording the image on the printing plate on the basis of the print image data obtained by the addition of the color chart data; a color chart position computation section for computing a position to which the color chart data was added; a printing section for printing a print image and the color chart on printing paper by using the printing plate; an image data acquisition section for acquiring image data on an area including the color chart on the printing paper on the basis of the position to which the color chart data was added; and a color chart information determination section for determining color chart information about each of color chart fields in the color chart on the basis of the image data.
In the tenth aspect, image data on an area including the color chart can be obtained on the basis of the position of the color chart in image recording, which allows proper color chart measurement.
An eleventh aspect of the present invention is directed to a color chart measuring apparatus for capturing an image on printing paper on which a color chart having a plurality of color chart fields was printed and measuring color chart information. The measuring apparatus comprises: an imaging section for reading an image on the printing paper being transported; a reading time setting section for determining, in accordance with a transport operation of the printing paper, a reading time during which the imaging section reads an image of the color chart; an image data storage section for storing image data on an area read by the imaging section during the reading time, as readout image data; a color chart actual position calculation section for calculating an actual position in which each of the color chart fields was actually printed, on the basis of the readout image data; and a color chart information determination section for determining the color chart information about each of the color chart fields from the readout image data corresponding to the actual position.
In the eleventh aspect, the imaging section can read only an area including the color chart, which reduces the amount of image data to be handled. Further, the use of a preset color chart avoids the necessity of preparing a reference image for comparison.
According to a twelfth aspect of the present invention, in the color chart measuring apparatus of the eleventh aspect, the reading time setting section acquires position information about the color chart from an image recording apparatus for recording the color chart on a printing plate, and determines the reading time on the basis of the position information.
In the twelfth aspect, the reading time to read the color chart can appropriately be determined according to the recording position of the color chart in image recording.
A thirteenth aspect of the present invention is directed to a color chart measuring method for use in a printing process for recording a print image and a color chart having a plurality of color chart fields on a printing plate and printing the color chart in a margin of printing paper by using the printing plate. The measuring method comprises the steps of: computing a position of the color chart relative to the print image; determining an area to capture an image of the color chart on the basis of the position of the color chart; imaging the area on the printing paper; storing readout image data obtained through imaging; computing an actual position of each of the color chart fields from the readout image data; and determining color chart information on the basis of the readout image data corresponding to the actual position.
In the thirteenth aspect, the reading time to read the image data can be determined from the position of the color chart relative to the print image, which reduces the amount of image data to be read.
A fourteenth aspect of the present invention is directed to a color chart measuring method for use in a printing process for recording a print image and a color chart having a plurality of color chart fields on a printing plate and printing the color chart in a margin of the printing paper by using the printing plate. The measuring method comprises the steps of: computing a position of the color chart relative to the print image; capturing an image on the printing plate; determining an area in which the color chart is located, on the basis of the position of the color chart; out of readout image data obtained through imaging, specifying readout image data on the area in which the color chart is located; computing an actual position of each of the color chart fields on the basis of the specified readout image data; and determining color chart information from the readout image data corresponding to the actual position.
In the fourteenth aspect, image data on only an area including the color chart can be determined from the position of the color chart relative to the print image, which reduces the amount of image data to be handled in image processing.
According to a fifteenth aspect of the present invention, in the printing press of the first aspect, the color chart is provided along a width of the printing paper for checking at least an ink density in the printing press, the color chart includes: at least two reference marks located at a predetermined distance from each other in a direction of a print span; and a plurality of kinds of color chart fields provided in a line between the reference marks, wherein the reference marks have a pattern to indicate positions of the color chart fields with respect to a print direction.
In the fifteenth aspect, a tilt of the color chart imaged can be corrected by using at least two reference marks, which is effective when making color chart measurement while transporting printing paper. Since the reference marks each have a pattern to indicate the positions of the color chart fields with respect to the print direction, the detection of the reference marks facilitates the specification of the position of the color chart.
A sixteenth aspect of the present invention is directed to a color chart measuring method for capturing an image of a color chart having a plurality of color chart fields on printing paper and measuring color chart information on the basis of image data obtained through imaging, wherein color data corresponding to each of the color chart fields is computed from image data on each of the color chart fields, and white color data corresponding to each of the color chart fields is computed from image data on an unprinted area in the close vicinity of each of the color chart fields; and in determining the color chart information on the basis of the image data on each of the color chart fields, a correction is made to the color data on each of the color chart fields on the basis of corresponding one of the white color data.
In the sixteenth aspect, white color correction can be made on the basis of image data on an unprinted area corresponding to each of the color chart fields. This allows a correction to be made on a difference in the imaging level which is caused by flapping or the like of printing paper.
According to a seventeenth aspect of the present invention, in the color chart measuring method of the sixteenth aspect, imaging of the color chart is carried out while the printing paper is being transported.
This is especially suitable for making color chart measurement while transporting printing paper.
According to an eighteenth aspect of the present invention, in the color chart measuring method of the seventeenth aspect, imaging of the color chart is carried out by means of an imaging section including a plurality of imaging devices, the imaging section reads a white reference object which was positioned at a standstill before the imaging of the color chart and uses the white reference object to make a shading correction on the image data.
In the eighteenth aspect, shading correction is made on the basis of a white reference object at a standstill, which improves the accuracy of color chart measurement.
A nineteenth aspect of the present invention is directed to a color chart provided along a width of printing paper for checking at least an ink density in a printing press. The color chart includes: at least two reference marks provided at a predetermined distance from each other in a direction of a print span; and a plurality of kinds of color chart fields arranged in line between the reference marks, the reference marks each have a pattern to indicate positions of the color chart fields with respect to a print direction.
In the nineteenth aspect, a tilt of the color chart imaged can be corrected by using at least two reference marks, which is effective when making color chart measurement while transporting printing matter. Since the reference marks each have a pattern to indicate the positions of the color chart fields with respect to the print direction, the detection of the reference marks facilitates the specification of the position of the color chart.
According to a twentieth aspect of the present invention, in the color chart of the nineteenth aspect, an unprinted area is formed adjacent to the color chart fields on the printing paper, and the reference marks each further has a pattern to indicate a range of the unprinted area.
In the twentieth aspect, a white reference can be produced from an unprinted area. Further, since the reference marks each have a pattern to indicate the range of the unprinted area, the detection of the reference marks facilitates the specification of the position of the unprinted area.
According to a twenty-first aspect of the present invention, in the color chart of the nineteenth aspect, of the at least two reference marks, two reference marks are provided at about both ends of the printing paper across the width of the printing paper.
In the twenty-first aspect, the reference marks are provided at about both ends of printing paper across the width, which improves the accuracy of tilt correction.
According to a twenty-second aspect of the present invention, in the color chart of the nineteenth aspect, some of the plurality of kinds of color chart fields are arranged on both sides of any one of the at least two reference marks in symmetry with respect to a point about the any one reference mark.
In the twenty-second aspect, the color chart fields are arranged symmetrically with respect to a point about a reference mark. Using that reference mark as a reference therefore facilitates calculation of the positions of the respective color chart fields.
According to a twenty-third aspect of the present invention, in the color chart of the nineteenth aspect, the color chart fields are of multiple colors (YMCK), and the reference marks are of a single black (K) color.
In the twenty-third aspect, since the reference marks are of a single black color, it is easy to detect or visually recognize the positions of the reference marks.
A twenty-fourth aspect of the present invention is directed to a color chart measuring method for measuring the color chart of the nineteenth aspect, comprising the steps of: obtaining image data by imaging an area including the color chart on the printing paper; computing positions of the reference marks from the image data; computing a position of each of the color chart fields on the basis of the positions of the reference marks; and measuring each of the color chart fields on the basis of the position of each of the color chart fields, wherein a tilt of the image data obtained by reading the color chart is corrected on the basis of the positions of the at least two reference marks.
In the twenty-fourth, a tilt of the color chart imaged can be corrected by using at least two reference marks. This is especially effective for a tilt of printing paper due to transportation, when color chart measurement is made while printing matter is being transported.
According to a twenty-fifth aspect of the present invention, in the color chart measuring method of the twenty-fourth aspect, when the color chart includes three or more reference marks, imaging is carried out by using a different line sensor for every two adjacent reference marks out of the three or more reference marks.
In the twenty-fifth aspect, even when a plurality of line sensors divide the color chart for measurement, each of the sensors can make tilt correction by using two reference marks.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.